a) Internal resistance

a) source of e.m.f.; internal resistance

b) terminal p.d.; lost volts

ci) the equations ε = I(r + V) and ε = V + r

terminal pd = the pd measured across the terminals of the emf source

internal resistance = the resistance within an emf source

when there is current in an emf source

• emf source transfers chemical energy to the electrical store of the charge carriers

• some chemical energy is dissipated into thermal energy

• internal resistance

• lost volts

relationship between terminal pd and emf

• → terminal pd < emf

• → emf = terminal pd + lost volts

• when current is 0A → emf = terminal pd

lost volts = Ir

• lost volts (V) = current (A) × internal resistance (Ω)

ε = I(R + r)

• emf (V) = current (A) × (resistance (Ωs) + internal resistance (Ω))

ε = V + Ir

• emf (V) = terminal pd (V) + (current (A) × internal resistance (Ω))